This present invention relates to generating data for volume rendering or multi-planar reformatting (MPR). MPR and volume rendering are provided for medical images, such as diagnostic ultrasound images. To represent the volume, ultrasound data representing a plurality of spaced apart planes is acquired. Large datasets composed of tens or hundreds of images or frames of data are acquired. Each image or frame is composed of a grid of samples. The samples are spaced in an acquisition format (e.g., polar coordinate or cylindrical coordinate format) or in an imaging format (e.g., Cartesian coordinate). A stack or collection of such data represents a grid-like array in a volume.
The volume rendering or MPR may require resampling the volume data into a uniform Cartesian grid. This Cartesian grid uses a right-handed coordinate system in which the x-axis is along the azimuth dimension of the probe, the y-axis is along the elevation dimension of the probe, and the z-axis points away from the probe face at the center of the array. The range along scan lines may be different than the z-axis. The uniform grid is isotropic, such that the grid points are regularly spaced along each of three dimensions. The ultrasound data may be interpolated to represent the uniform Cartesian grid rather than the acquisition or imaging grids. Typically, the eight ultrasound samples nearest to a grid point are selected and trilinearly interpolated to form the voxel value for the grid point. Where the data of the different planes is aligned, the same x and z coordinates may be input for selecting data from different planes. However, ultrasound data acquired in an irregular pattern may result in memory calls to the wrong data. The reconstruction to the uniform Cartesian grid may not be correct.
U.S. Published Patent Application Nos. 2008/0125659, 20080125661, and 20090010459, and U.S. Pat. No. 7,678,056 disclose acquiring data for a volume with a helical array. By walking an aperture along the helical array, different planes are scanned. Due to the helical positioning of the apertures, different planes are not aligned in azimuth-range. Because of the irregular sampling grid, using hardware-accelerated trilinear interpolation may result in image artifacts in volume-rendered and multi-planar reformatted images. A standard trilinear interpolation kernel that fetches adjacent samples by incrementing the range, azimuth, and elevation addresses of an anchor sample by one unit may not select the proper azimuth addresses if the azimuth shift between slices is greater than one acoustic line width. Such problems may exist for other irregular sampling grids.